He uses the air rifle incorrectly (5)
I believe the answer is:
flier
'he uses the air' is the definition.
(a flier uses the air to travel in)
'rifle incorrectly' is the wordplay.
'incorrectly' is an anagram indicator (I've seen this in other clues).
'rifle' is an anagram of 'FLIER'.
(Other definitions for flier that I've seen before include "Turkey perhaps?" , "Advertising leaflet" , "Rifle for airman" , "Aviator" , "PO, for example" .)